For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane. The electrolyte membrane is interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell for generating electricity. In use, normally, a predetermined number of unit cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the separators for supplying a coolant along surfaces of the separators.
In this regard, the fuel cell may adopt internal manifold structure in which fuel gas passages for flowing a fuel gas therethrough, oxygen-containing gas passages for flowing an oxygen-containing gas therethrough, and coolant passages for flowing a coolant therethrough are formed in the fuel cell and extend through the fuel cell in the stacking direction.
As a fuel cell of this type, for example, a fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2006-172924 is known. As shown in FIG. 10, a separator 1 disclosed in Japanese Laid-Open Patent Publication No. 2006-172924 includes a fuel gas flow field 2. The fuel gas flow field 2 includes a main flow field 3 connected to an inlet manifold 6a and an outlet manifold 6b through a distribution section 4 and a merge section 5.
The main flow field 3 is divided by a plurality of ribs 7a, and the distribution section 4 and the merge section 5 are divided by a plurality of ribs 7b, 7c. The ribs 7b, 7c are divided respectively by disconnected portions 8a, 8b in the middle in the longitudinal direction. The disconnected portions 8a, 8b of the ribs 7b, 7c are shifted from disconnected portions 8a, 8b of the adjacent ribs 7b, 7c in the longitudinal direction of the separator 1.